7.1.2. Investigating thermotactic behaviour

One approach to
investigate the dynamics of the honey bees' winter cluster, for example, is to
model honey bee thermoregulation. These modelling studies readily assume a
direct uphill/downhill approach of honey bees towards a temperature optimum
(Sumpter and Broomhead, 2000). Although studies on the location of sensory
organs necessary for such a direct gradient ascent/descent were performed
decades ago (Lacher, 1964), little is known about the proximate mechanisms of
thermotaxis of honey bees in temperature fields. Early experiments in a
so-called "temperature organ" (Fig. 9; Herter, 1924; Heran, 1952)
have indicated that the outer two segments of the bee antenna are the most
important locations for the temperature sense of the honey bee. However, such
"temperature organs" are only a very rough approximation of the inner
climate of a honey bee colony. They can only generate simple steep gradients in
an almost one-dimensional environment. In contrast to that, the inner space of
a honey bee colony is a complex three-dimensional structure and every comb the
bees crawl on can be interpreted as a two-dimensional space.

Fig. 9.The
classical temperature organ according to Herter. Bees move in a one-dimensional
thermal gradient in the central tunnel (l = 53 cm) until they find the spot of
their preferred temperature. To establish the gradient, the tunnel is heated by
a hot water bath at the left side and cooled by ice contained in the box to the
right. The thermometers at the back survey the gradient.